An impulse is a signal from the subconscious influencing one to behave in a particular way. It is the result of a subconscious calculation of the expected pleasure to be received, or pain avoided, by taking a specific course of action.

A compulsion is an extremely powerful impulse.

Pain and pleasure are not necessarily mutually exclusive. Some situations offer both, complicating some choices.

While human impulses may not be exactly the same as the impulses of members of other animal species, the function of impulses to direct behavior is a part of our common heritage (at least among animals with brains).